Polyolefin resins are commonly used as a material in the sheath layers of wires and cables, e.g., the insulation or outer jacket surrounding the wire or cable. Additives are commonly blended with the polyolefin resins to impart flame retardancy to these sheath layers. Typical additives include organic halogenated compounds and flame retardant synergists, such as antimony trioxide. Unfortunately, these additives can cause smoking and/or the emission of harmful gases when subjected to burning. These additives can also cause metals to corrode.
To address these issues, the halogenated flame retardant is often replaced with a non-halogenated or halogen-free flame retardant, such as a metal hydroxide. While addressing the smoking and harmful gas issues, the use of halogen-free flame retardants has some undesired effects. One issue with halogen-free flame retardants is that a relatively larger amount of flame retardant filler is required to achieve the same level of flame retardance as that achieved when using a halogenated flame retardant. The higher content of halogen-free flame retardant can adversely affect the polyolefin resin in terms of melt extrudability, mechanical properties, flexibility, and low temperature performance. In particular, with ethylene vinyl acetate copolymer-based compositions, the higher content of halogen-free flame retardant causes the melt viscosity to increase and tensile elongation to decrease, both of which are undesirable.
Therefore, halogen-free flame retardant compositions with balanced and improved melt rheological, tensile, and flame-retardant properties are desirable.